One of the most important du'a is, "Allah make us love iman and make it beautiful in our hearts. And make hated to us kufr (disbelief), fusuq (deviance) and 'isyan (disobedience)."
Corollary to this is the verse, "We created everything in pairs" and the hadith "Islam, Iman, Ihsan."
Everything has either a complementary pair (didd) or a mutually exclusive opposite (naqid). If we love one thing, then by necessity we must hate the thing that negates our love, i.e. its mutually exclusive opposite. A woman cannot love her husband while simultaneously loving that which pulls him away from her, such as the idea of him being tempted by another woman. Similarly, one cannot love democracy and dictatorship simultaneously.
In the same vein, Prophet Isa said, iman and kufr in one heart are like water and fire in the same vessel: one will eventually negate the other.
The opposite of Islam is kufr. The opposite of iman is deviance (bida'). The opposite of ihsan is disobedience.